1. Field
The present disclosure relates generally to radio frequency (RF) switching and, more specifically, to transistor-based RF switch stacks.
2. Background
Electronic switches are commonly based on transistors, such as field-effect transistors (FETs). In RF applications such as mobile phones, which have high RF transmission output power, the RF voltage swing can be higher than the maximum voltage that one single FET can handle. As illustrated in FIG. 1, a conventional device 10 for switching RF signals includes two or more FETs 12, 14, 16, 18, etc., connected in a stack or chain topology in which the source terminal of a FET is connected directly to the drain terminal of an adjacent FET in the chain. In FIG. 1, further FETs in the chain between FETs 16 and 18 that are not shown for purposes of clarity are indicated by the ellipsis symbol (“ . . . ”). The gate node of each of FET 12-18, etc., is connected to a gate bias network 20, which also receives a switch control signal as an input. In response to the switch control signal, device 10 opens or closes a circuit between a first RF signal node (“RF1”), which is defined by the source node of the last FET 18 in the chain, and a second RF signal node (“RF2”), which is defined by the drain node of the first FET 12 in the chain. Device 10 is commonly referred to as a “switch stack” or “FET stack.”
As illustrated in FIG. 2, a conventional device 22 similar to above-described device 10 includes two or more FETs 24, 26, 28, 30, etc., connected in the above-described stack or chain topology. The gate nodes of FETs 24-30, etc., are connected to a gate bias network 32 similar to above-described gate bias network 20. Each of FETs 24, 26, 28, 30 etc., also includes a body node that is connected to a body bias network 34. As understood by one of ordinary skill in the art, some semiconductor technologies, such as partially depleted silicon-on-insulator (“SOI”), provide such a body node, while others, such as gallium arsenide (“GaAs”) pseudomorphic high-electron mobility transistor (“pHEMT”) and floating-body and fully depleted SOI, do not provide such a body node. Devices that provide a FET body node are commonly called body contact devices. Although not shown, a drain-source bias network, such as a resistor between the drain and source nodes of each of FETs 24, 26, 28, 30, etc., is also commonly included, and may be considered part of gate bias network 32 or body bias network 34.
The performance of switch stacks in mobile phone RF front end circuitry, such as the receive/transmit (“Rx/Tx”) switch, is adversely affected by poor linearity. Linearity of a switch stack, as well as power handling capability, can be increased by increasing the number of FETs in the stack or chain. However, increasing the number of FETs can increase RF loss and decrease manufacturing economy.